CT DEEP Stormwater General Permit: Types, ezFile, and Compliance

A CT DEEP stormwater general permit is required before stormwater leaves your property and enters state waters if you are running a construction project that disturbs one acre or more, an industrial facility with exposed operations, a commercial site with five or more acres of impervious surface, or a municipal storm sewer system. The Department of Energy and Environmental Protection issues four separate general permits under Connecticut General Statutes sections 22a-430 and 22a-430b, and each one carries its own eligibility rules, planning documents, and ongoing obligations.¹² Picking the wrong one delays your project and can expose you to enforcement, so the first job is figuring out which category you fall into.

Which Permit Applies to Your Site

Construction

The construction permit covers land disturbance of one acre or more, and Connecticut splits covered projects into three registration categories based on who is doing the work and how much ground is moving. Private projects between one and five acres are “locally approvable small construction” and go through municipal review by a planning, zoning, wetlands, or conservation commission rather than a state application. Private projects disturbing five acres or more are “locally approvable large construction” and need both local municipal approval and a state general permit registration filed with CT DEEP. Government projects (municipal, state, or federal) disturbing one acre or more are “locally exempt,” meaning they skip local review but must register directly with CT DEEP.³

A small private subdivision on three acres never touches the state permitting system. A state highway project on the same acreage goes straight to CT DEEP. Misidentifying the category is a common early mistake.

Industrial

The industrial permit applies to facilities whose operations could expose pollutants to stormwater, categorized by Standard Industrial Classification (SIC) and North American Industry Classification System (NAICS) codes. Sectors like scrap recycling, transportation, and chemical manufacturing face standards written for their specific pollutant profiles.⁴ If stormwater at your facility never contacts industrial materials, equipment, or activities, you can file a No Exposure Certification instead of a full registration, which significantly lightens the compliance load.

Commercial

Commercial sites with five or more acres of contiguous impervious surface, such as shopping malls, movie theaters, and large supermarket complexes, must register under the commercial permit. The site must also have a primary activity matching one of the eligible SIC or NAICS codes in the permit, and its discharge cannot already be covered by another permit.⁵ The threshold is five acres, not more than five. A site with exactly five acres of impervious cover is already in.⁶

MS4 (Municipal Separate Storm Sewer System)

Municipalities, public universities, and certain state and federal facilities that operate storm sewer systems fall under the MS4 permit. Each covered entity must develop a Stormwater Management Plan describing how it will meet permit requirements, post the plan for public review, and submit annual reports to CT DEEP by April 1.⁷ The annual review fee is $187.50 for municipalities and $375 for institutions.⁸

The Stormwater Pollution Control Plan

Every registration requires a Stormwater Pollution Control Plan (SPCP), Connecticut’s version of what the federal system calls a SWPPP. A weak or incomplete SPCP is the fastest way to stall a registration or fail an inspection. At a minimum it must include:

A project description and construction sequencing narrative, with erosion and sediment controls tied to each phase and an estimated timeline.
Site description: total site area, expected area of disturbance, average post-construction runoff coefficient, name of the receiving waterbody, and wetland acreage on site.
Site plan drawings showing drainage patterns, slopes, disturbance areas, and all structural and non-structural control locations.
Every discharge outfall where stormwater leaves the site.
Design factors: expected precipitation, impervious surface runoff, soil types and particle sizes, and proximity to wetlands, vernal pools, and surface waters.

For locally approvable large construction and locally exempt projects, the SPCP must be prepared by a qualified professional. Large private projects also require certification by a qualified professional or a Soil Conservation District.³ The commissioner has broad statutory authority to set qualified professional credentials, including education, training, experience, licensing, and independence from conflicts of interest.² Small construction projects of one to five acres need only a local erosion and sediment control plan reviewed by the municipality.

Industrial facilities must develop an SPCP or equivalent pollution prevention plan at registration. It has to be signed by a duly authorized representative, kept on-site, and made available to the commissioner or to the operator of any connected municipal storm sewer system.

Registering Through ezFile

All stormwater registrations go through CT DEEP’s ezFile portal.⁹ You create an account, select the stormwater permit type from the left menu, upload your SPCP and supporting documents, and pay the fee through the portal.¹⁰

Fees vary by permit type. Industrial stormwater is either $625 or $1,250 depending on employee count and gross sales, with municipalities paying 50% of the standard rate.⁴ Construction and commercial fees depend on category and project size. All fees are non-refundable.

CT DEEP estimates processing at either 60 or 90 days depending on the registration category.³ Emergency construction activity is the exception, with immediate authorization to prevent danger or restore essential services. After submission you receive a tracking number that serves as your reference for all agency correspondence. Do not begin discharge activities until you have received authorization, unless your project falls under the emergency exception.

Inspection and Reporting After You Are Permitted

Getting the permit is the easy part. Staying compliant is where most permittees get into trouble.

Construction sites must be inspected at least once a week and within 24 hours after any storm that generates a discharge. The inspector must examine all disturbed areas not yet stabilized, discharge outfalls, dewatering discharges, erosion and sediment controls, soil stockpiles, washout areas, and vehicle entry and exit points. When possible, the inspection should happen during an active rain event. For storms that end on weekends or holidays, the 24-hour window applies only to storms of half an inch or more; smaller storms can wait until normal working hours resume. Once temporary stabilization is in place, weekly inspections continue until final stabilization is achieved, at which point the schedule drops to monthly. Every inspection has to be documented in a written log kept on-site, with any control failures and corrective actions recorded.

Industrial permit holders must sample their discharges and submit results electronically. EPA requires industrial facilities to use the NetDMR system for all discharge monitoring reports, which transmits data directly to state and federal databases.¹¹

MS4 permittees submit annual reports summarizing progress on the Stormwater Management Plan. The report must be posted for public review and comment by February 15, then submitted to CT DEEP by April 1.⁷ Commercial permittees face similar annual reporting on maintenance activities and drainage system improvements.

Post-Construction Standards That Outlast the Project

Connecticut’s stormwater rules do not end when construction wraps. The state’s Stormwater Quality Manual sets five performance standards for development and redevelopment after construction is complete.

The most consequential standard requires retaining on-site the applicable post-development runoff volume, calculated using a water quality storm variable of 1.3 inches (increased from the previous 1-inch standard). Where full retention is not achievable, the remaining volume must receive treatment before discharge. Low-impact development techniques such as bioretention areas, permeable pavement, and vegetated swales must be considered early in site planning.¹²

Peak runoff must also be managed. The two-year post-development flow rate cannot exceed 50% of the predevelopment rate, and the ten-year post-development rate must stay at or below the predevelopment rate. Every project needs a long-term operation and maintenance plan identifying inspection and maintenance schedules for all structural stormwater controls. Retrofitting a site to hit retention standards after the fact is far more expensive than designing for them from the start.

Transferring or Terminating Coverage

When a permitted site changes hands, the new owner cannot simply pick up under the existing permit. Both the current licensee and the proposed transferee must submit a License Transfer Form and applicable fee within 30 days of the transfer. CT DEEP reviews the transferee’s ability to comply, and the transferee cannot conduct the permitted activity until DEEP sends written confirmation approving the transfer. A transferred permit only authorizes the activities described in the original permit; new activities or operational changes need a modification or a new permit.¹³

Terminating a construction permit requires filing a Notice of Termination (NOT) with the commissioner. A project qualifies for standard termination when all post-construction measures are installed, functioning, inspected, and cleaned, and the site has achieved final stabilization for at least one year. That one-year stabilization requirement catches developers off guard because the permit stays active well beyond the last day of construction. When a project transfers to a new permittee, the original permittee must file a NOT within 30 days of the new authorization.³

What Noncompliance Costs

The financial consequences are severe. The Clean Water Act’s base statutory penalty of $25,000 per day per violation has been adjusted for inflation and now stands at $68,445 per day for violations assessed on or after January 8, 2025.¹⁴ A site with multiple deficiencies can rack up six-figure liability in a single week. Connecticut also has independent enforcement authority under its own statutes, so state and federal agencies can pursue violations at the same time.¹

Beyond fines, CT DEEP inspectors conduct unannounced site audits. Consistent record-keeping, an up-to-date SPCP, and documented inspection logs are your best protection. The registrants who get into serious trouble are almost always the ones who treated the permit as a one-time filing rather than an ongoing obligation.

1
Justia. Connecticut General Statutes 22a-430 – Permit for New Discharge
2
Justia. Connecticut Code 22a-430b – General Permits, Certifications by Qualified Professionals, Regulations
3
Connecticut Department of Energy & Environmental Protection. Construction Stormwater General Permit
4
Connecticut Department of Energy & Environmental Protection. Industrial Stormwater GP
5
Connecticut Department of Energy & Environmental Protection. Commercial Stormwater
6
Connecticut Department of Energy and Environmental Protection. General Permit for the Discharge of Stormwater Associated with Commercial Activity
7
Connecticut Department of Energy & Environmental Protection. Municipal Stormwater
8
CT NEMO Program. Annual Reports
9
Connecticut Department of Energy & Environmental Protection. Welcome to DEEP’s ezFile Portal
10
Connecticut Department of Energy and Environmental Protection. Getting Started with DEEP’s ezFile Portal
11
Environmental Protection Agency. Stormwater Discharges from Industrial Activities-Electronic Reporting
12
CT NEMO Program. Chapter 4: Stormwater Management Standards and Performance Criteria
13
Connecticut Department of Energy & Environmental Protection. Permit Transfer Fact Sheet
14
eCFR. 40 CFR 19.4 – Statutory Civil Monetary Penalties, as Adjusted for Inflation